Process for the manufacture and sizing of float glass

ABSTRACT

A process for the manufacture of sheet glass which involves flowing a controlled amount of molten glass down an inclined plane onto and along the upper surface of a bath of molten metal. The molten glass is sized by passing it beneath a sizing member which extends widthwise of the bath and which has at least the portion thereof facing the molten glass layer passing thereunder composed of a porous and permeable material. Producer gas or hydrocarbon gas is introduced into the sizing member and is blown out through the porous and permeable portion thereof to form and maintain a burning gaseous film between the surface of the sizing member and the molten glass layer.

United States Patent Kita et a1.

PROCESS FOR THE MANUFACTURE AND SIZING OF FLOAT GLASS Inventors: HideoKita, Amagasaki-shi; Kunihiko Ito, Nishinomiya-shi, both of Japan NipponSheet Glass Co., Ltd., Osaka, Japan Assignee:

Notice: The portion of the term of this patent subsequent to May 6,1986, has been disclaimed.

Filed: Dec. 12, 1968 Appl. No.: 785,048

Related US. Application Data Continuation of Ser. No. 479,548, Aug. 13,1965 abandoned.

Field ofSearch ..65/25 A,91, 65 A, 99 A, 182, 65/169, 92

References Cited UNITED STATES PATENTS 6/1930 Mambourg ..65/91 2,387,88610/1945 Devol r ..65/25 2,444,731 7/1948 Devol ..,..65/25 2,478,0908/1949 Devol .....65/25 2,505,103 4/1950 Devol ..65/25 3,266,880 8/1966Pilkington ..65/99 1,827,138 10/1931 Brancart..... .65/25 A 1,841,5271/1932 Fraser MATS/92 1,841,576 1/1932 Drake ....65/92 3,442,636 5/1969Kim et a1. ..65/182 Primary Examiner-S. Leon Bashore AssistantExaminer-J. B. Hardaway Attorney-Wenderoth, Lind & Ponack 5 7] ABSTRACTA process for the manufacture of sheet glass which involves flowing acontrolled amount of molten glass down an inclined plane onto and alongthe upper surface of a bath of molten metal. The molten glass is sizedby passing it beneath a sizing member which extends widthwise of thebath and which has at least the portion thereof facing the molten glasslayer passing thereunder composed of a porous and permeable material.Producer gas or hydrocarbon gas is introduced into the sizing member andis blown out through the porous and permeable portion thereof to formand maintain a burning gaseous film between the surface of the sizingmember and the molten glass layer.

5 Claims, 15 Drawing Figures Pmmwmz me 3,637,361

sum 20! 2 INVENTOR 5 BY a/JM M dZ/GAJ MATTORNEY s PROCESS FOR THEMANUFACTURE AND SIZING F FLOAT GLASS This is a streamlined continuationof application Ser. No. 479,548 filed Aug. 13, 1965, now abandoned.

The present invention relates to a process for the continuousmanufacture of sheet glass.

Various processes have been practiced for the manufacture of sheet glasscontinuously. For example, there is a process of drawing molten glassupwardly from the free surface of a molten bath or through a refractoryslit. Also a process of sizing molten glass by means of a pair of metalrollers is known. The molten glass so rolled between a pair of metalrollers may be reheated on a molten metal bath. Furthermore, there isalso a known process wherein molten glass is directly flowed onto amolten metal bath without a preceding sizing operation so it can bereheated and drawn under a suitable tension.

However, the above known'processes each have deficiencies inherenttherein. To wit, the process of upwardly drawing molten glass does notproduce sheet glass of a uniform thickness, and the drawing speed cannotbe raised over a certain limit. In the process of sizing molten glass bymeans of a pair of metal rollers, the glass surfaces after the sizingtend to have numerous fine uneven portions due to shrinkage because themolten glass having a high temperature is quenched by the water-cooledmetal rollers, or unevenness caused by the scale fon-ned on the surfacesof the rollers, and thus smooth, lustrous and transparent sheet glasscannot be obtained. The process of reheating the sized glass consumes alarge amount of fuel or electricity, and for reducing the unevenness inthe glass surface to a satisfactory degree, a vary long molten metalbath is required. The process of letting molten glass flow onto a moltenmetal bath without sizing can avoid such deficiencies caused by thesizing but the controlling of the amount of molten glass flowed andconsequently of the thickness of the resultant sheet glass by means of arefractory damper is difficult. Therefore, sheet glass having a desireduniform thickness throughout its width can not easily be obtained bythis process, and in order to make uniform the thickness of the productthe sheet glass must be maintained on a molten metal bath at a very hightemperature for a long time. For this purpose a vary long molten metalbath is required, and the consumption of fuel or electricity thereforbecomes great.

We previously proposed, as a process for the manufacture of sheet glassfree from the above-described deficiencies inherent in the conventionalart, a process wherein molten glass is allowed to flow down an inclinedplane continuously and immediately thereafter to pass between a metalroller and the upper surface of a bath of molten metal to be sizedthereby, under the pending Japanese Patent Application No. 69417/1963.

However, even by that improved process the formation at the time ofsizing of small amounts of unevenness in the glass surface coming indirect contact with the metal roller cannot be completely avoided, asthe surface is quenched by the roller. Also the surface of the roller isapt to be contaminated by glass. Therefore as a process for easilyobtaining smooth, lustrous sheet glass, our previously proposed processcannot be said to be entirely satisfactory.

It has now been found that the above-described deficiencies anddisadvantages in the prior art can be overcome by a process wherein acontrolled amount of molten glass is allowed to flow down an inclinedplane and led to a space between a sizing means, of which at least theportion facing the glass layer passing thereunder is composed of aporous and permeable material, and the upper surface of a bath of moltenmetal, and a gas under pressure introduced into the sizing means isblown out through the portion of the sizing means facing the moltenglass layer passing thereunder, to form and maintain a thin film of thegas between the surface of the sizing means and the glass so that theglass is sized between the gaseous film and the upper surface of thebath of molten metal.

Referring to the attached drawings, F IG. 1 is a vertical sectional viewof an apparatus suited to practice the process of this invention; FIGS.2 and 3 are partial vertical sectional views showing modifications ofthe apparatus of FIG. 1; FlGS. 4 and 4', 5 and 5, 6 and 6', and 7 and 7illustrate various sizing means suited for use in practicing the processof this invention; FIG. 8 is a vertical sectional view of a differentapparatus suited to carry the sized sheet glass; FIGS. 9.and 9' are planand sectional elevation views illustrating an embodiment of dividedsizing means; and FIG. 10 is a transverse section along the line I[ inFIG. 9.

Referring to FIG. 1, the molten glass 1 leaves the forehearth 2 ofamelting tank and flows down on a lip tile 3 and is led to a spacebetween the sizing means 4 and the upper surface of a bath 5 ofa moltenmetal. The amount of the, molten glass flowing can be controlled bymeans ofa vertically movable damper 6 provided at the exit of theforehearth 2.

The sizing means 4 is composed of porous and permeable graphite, and itsstructure is shown in FIGS. 4 and 4. The graphite used herein has aporosity of about 30 percent. The sizing means maybe substantiallyentirely composed of a porous material, but it is sufficient that thelower portion thereof, i.e., the portion facing the molten glass, is ofa porous and permeable structure. For the porous portion of the sizingmeans, such refractory materials as high-aluminous refractory, sinteredsilicon carbide and the like, and sintered alloys may be used as well asgraphite. The surfaces of the' porous portion should preferably befinished. The sizing means may be stationary or may be rotatable like aroller. In case of the latter, the entire surface thereof must be of theporous structure. One embodiment in which the porous sizing means is ofthe form of a roller is shown in FIGS. 2, 5 and 5. The sizing means maybe a water-cooled structure as shown in FIGS. 6, 6, 7 and 7. FIGS. 9, 9and 10 show one embodiment of a sizing means which is divided in thedirection of the width thereof consisting of a plurality of small sizingmeans, in which 16 denotes each of the small sizing means which are allvertically movable, 17 is the adjustment rod for vertically moving thesmall sizing means l6, 18 is a conduit for introducing a gas underpressure, 19 is a portion made of heat-resisting steel and 20 is theportion made of a porous material. When such a sizing means is used, thethickness of the product in the direction of the width of the sheetglass can be made uniform more easily than when using a nondividedsizing means, by detecting the thickness of the sized sheet glass atpoints across its width and automatically and precisely controlling thevertical positions of the small sizing means in accordance therewith.The metal used for the bath 5 must have a higher specific gravity in themolten state than that of the molten glass, and must be nonreactablewith the molten glass. Metals having a melting point no higher thanabout 600 C. and a boiling point no lower than about l,l00 C., such astin, lead, alloys of tin and lead or of tin and aluminum are useful,particularly tin being preferred. The temperature of the molten metal inthe bath should be maintained at about 900- l C.

The molten glass is continuously sized by being subjected to theinfluence of buoyancy caused by the difference in specific gravities ofthe molten metal of the bath 5 and the glass, as well as to the downwardpressure of the sizing means 4. The level of the sizing means relativeto the upper surface of the bath 5 is suitably controlled-depending onthe desired thickness of the product sheet glass and the specificoperating conditions such as theamountof flow and the temperature of theglass and the rate of transfer of the sheet glass.

During the sizing of the molten glass between the porous sizing means 4and the upper surface of the bath 5, a gas at a predetermined pressureand temperature is introduced into the sizing means 4, so that a thinfilm of the gas will be formed and maintained between the surfaces ofthe sizing means and the molten glass layer. When the porous sizingmeans is made of graphite, nitrogen gas is suitable for this purpose,whereas when it is of a refractory materiaL'air or a combustible gase.g., producer gas, a hydrocarbon gas such as propane or butane issuitable. Such a combustible gas burns on the surface of the sizingmeans and therefore performs so-called firepolishing simultaneously withthe sizing when it is used in this invention, and thereby enables theproduction of sheet glass having highly lustrous and smooth surfaces.

The pressure of the gas to be introduced into the sizing means should bedetermined depending on the resistance of the sizing means totransmission of the gas, i.e., permeability and thickness of the porousportion thereof. In case the porous portion has a porosity on the orderof 203l0 percent, generally a pressure of the gas of about 1-3 kg./cm.is satisfactory. When the pressure of the gas is too high, objectionablecords tend to appear in the glass, while if it is too low, the glasstends to adhere to the sizing means. Those who are reasonably skilled inthe art should be able to easily determine the optimum pressure of thegas in each specific case for forming and maintaining a thin gaseousfilm between the surfaces of the sizing means and of the glass layer byexperiments.

It is recommended that the gas to be introduced into the sizing meansshould be preheated to a temperature as close as possible to that of theglass to be sized. The amount of flow of the gas may be relativelysmall, and in most cases an amount of about 60 em /min. per one squarecentimeter of the surface area of the porous and permeable portion ofthe sizing means (at the standard condition of C. and 760 mm. Hg) orless is satisfactory.

In case graphite is employed as the porous material for the sizingmeans, even when a high-purity nitrogen gas is used, erosion of graphitesometimes takes place'due to the oxidizing nature of the atmosphere ofthe sizing means or impingement of an exhaust gas from the glass-meltingfurnace or the molten metal bath against the sizing means. Therefore,provision of a chamber 21 filled with a protective gas (N around thesizing means is recommended for the prevention of such possible erosionof graphite.

The sheet glass 9 as sized is subsequently cooled by a cooling tank 10to about 600 C., and thereafter is carried away by means of a rollerconveyor 11. At such a temperature the glass is already sufficientlysolidified so the surfaces thereof are not damaged by contact with themetal rollers. In FIG. I the cooling tank 10 consisting of cooling bathsl2, l3 and 14 of tin the temperatures of which are controlled to havesuccessively lower temperatures in the stated order shown. This is notthe sole possible structure, but modifications thereof are possible. Forexample, instead of using the cooling tank 10, the glass may be carriedaway while being supported by air jetted against the glass, while thetemperature of the said air is regulated to perform the cooling of theglass (FIG. 8). In FIG. 8, 15 is a refractory flat plate having manypores on the surface thereof through which air is jetted upwards tosupport the sheet glass 9.

Furthermore, in place of the aforesaid damper 6 for regulating the flowof the molten glass, a damper 8 composed of a porous material similar tothe sizing means used in this invention may be adopted with an increasedeffectiveness (FIG, 3). Because, as the ordinary damper 6 tends to havethe molten glass adhere thereto, the flow of the glass from such adamper is not smooth and tends to produce objectionable cords therein.Whereas when the porous damper 8 is employed, such adhesion of the glassto the damper can be avoided, and so a smooth flow of molten glasshaving a substantially uniform thickness in the direction of its widthand which has the surface free from the above-mentioned defects can besent into the sizing means.

According to the present invention, the molten glass is sized betweenthe thin gaseous film formed and maintained on the surface of the sizingmeans and the upper surface of the molten metal bath, without a directcontact with, or being quenched by, the sizing means. 0n the other hand,the sizing means also is protected by the gaseous film fromcontamination by the glass or exhaust gas. Consequently, sheet glasshaving a highly smooth and lustrous surface can be very easily andcontinuously produced. In addition, as the bottom surface of the sheetglass is sized while being in contact with a high-temperature moltenmetal, the same is not quenched during the sizing, and so a very smoothbottom surface similar to the upper surface can be obtained.Furthermore, the sheet glass sized in accordance with-the process ofthis invention need not be reheated after the sizing, having alreadysatisfactory smooth surfaces. It is sufficient for the sheet glass sizedin accordance with the process of this invention to be subsequentlycooled on a bath of molten metal until it acquires a sufficient hardnessso that its contact with metal rollers of an ordinary roll conveyor doesnot damage the surface thereof. Therefore, in practicing the presentinvention, the length of the bath of molten metal used for this purposecan be very much shorter than that required for a conventional moltenmetal bath used for reheating sheet glass thereon, which has suchadvantages as reduction in equipment cost, floor area and cost of fuel.Again in accordance with the process of this invention. a product whichis too thin to be manufactured by the conventional processes using amolten metal bath can be readily obtained.

We claim:

1. A process for the manufacture of sheet glass comprising flowing acontrolled amount of molten glass down an inclined plane onto and alongthe upper surface of a bath of a molten metal, and sizing the moltenglass by the steps consisting essentially of positioning a sizing memberat the surface of the molten metal bath and extending widthwise of thebath and having at least the portion thereof facing the molten baththereunder and extending entirely across the molten bath composed of aporous and permeable refractory material, holding the sizing member in afixed position, passing the molten glass between the sizing member andthe molten metal bath, and introducing a combustible gas selected fromthe group consisting of producer gas and hydrocarbon gas into the sizingmember and blowing it out through the portion of the sizing memberfacing the molten glass layer to burn on the surface of the sizingmember and form and maintain a thin gaseous film between the entirewidth of the surface of the sizing member and the molten glass layer forsizing and fire-polishing the glass between the gaseous film and theupper surface of the bath of the molten metal without driving the glassby the sizing member, whereby the entire width thereof is smoothed andpolished, the refractory material of the sizing member beingnonconsumable by the combustion of the combustible gas.

2. The process as claimed in claim 1 in which the gas introduced intothe sizing means is blown out at the rate of up to about 60 cm, (atstandard temperature and pressure)/min. per square centimeter of thesurface area of the porous and permeable portion of the sizing means atthe standard state.

3. The process as claimed in claim I in which the porous and permeablematerial is a sintered alloy.

4. The process as claimed in claim I in which the gas is preheated to atemperature of the molten glass or a temperature close thereto.

5. A process for the manufacture of sheet glass comprising flowing acontrolled amount of molten glass down an inclined plane onto and alongthe upper surface of a bath of a molten metal, and sizing the moltenglass by the steps consisting essentially of positioning a rotatablesizing member at the surface of the molten metal bath and extendingwidthwise of the bath and extending entirely across the molten bath andthe entire sizing member being composed of a porous and permeablerefractory material, holding the sizing member with the axis of rotationat a standstill with respect to the advance of the glass, passing themolten glass between the sizing member and the molten metal bath, andintroducing a combustible gas selected from the group consisting ofproducer gas and hydrocarbon gas into the sizing member and blowing itout through the sizing member to form and maintain a thin gaseous filmbetween the entire width of the surface of the sizing member and themolten glass layer for sizing and fire-polishing the glass between thegaseous film and the upper surface of the bath of the molten metalwithout driving the glass by the sizing member and the entire widththereof is smoothed and polished, the refractory material of the sizingmember being nonconsumable by the combustion of the combustible gas.

2. The process as claimed in claim 1 in which the gas introduced intothe sizing means is blown out at the rate of up to about 60 cm.3 (atstandard temperature and pressure)/min. per square centimeter of thesurface area of the porous and permeable portion of the sizing means atthe standard state.
 3. The process as claimed in claim 1 in which theporous and permeable material is a sintered alloy.
 4. The process asclaimed in claim 1 in which the gas is preheated to a temperature of themolten glass or a temperature close thereto.
 5. A process for themanufacture of sheet glass comprising flowing a controlled amount ofmolten glass down an inclined plane onto and along the upper surface ofa bath of a molten metal, and sizing the molten glass by the stepsconsisting essentially of positioning a rotatable sizing member at thesurface of the molten metal bath and extending widthwise of the bath andextending entirely across the molten bath and the entire sizing memberbeing composed of a porous and permeable refractory material, holdingthe sizing member with the axis of rotation at a standstill with respectto the advance of the glass, passing the molten glass between the sizingmember and the molten metal bath, and introducing a combustible gasselected from the group consisting of producer gas and hydrocarbon gasinto the sizing member and blowing it out through the sizing member toform and maintain a thin gaseous film between the entire width of thesurface of the sizing member and the molten glass layer for sizing andfire-polishing the glass between the gaseous film and the upper surfaceof the bath of the molten metal without driving the glass by the sizingmember and the entire width thereof is smoothed and polished, therefractory material of the sizing member being nonconsumable by thecombustion of the combustible gas.